It had been identified that the male gamete-attracting substances secreted from female gametes of fied-grown Scytosiphon lomentaria was hormosirene. In this investigation, furthermore, with preventing contamination from volatile compounds formed from epiphytes and bacteria, S.lomentaria had been cultured. And it was revealed that the male gamete-attracting substance secreted from gametes of its was hormosirene. Similarly, it was elucidated that female gametes of field-grown and cultural Petalonia fascia, which is classified into same family of Scytosiphonaceae, as S.lomentaria, also secreted hormosiren as the male gamete-attracting substance.(-) (3R,4R) -3-butyl-4-vinylcyclopentene [(-) -1] was synthesized via (+) - (1S,5R) -3-oxabicyclo [3,3,0] oct-6-en-2-one. The synthetic (-) -1 coincided with the peak with later retention time of racemic (<plus-minus>) -1 in a chiral GC (CP-Cyclodex 236M), while the natural 1 in essential oils from the marine brown algae, Dicyopteris prolifera and D.sp.was identical with the earlier retention time peak. Thus, the absolute configuration of the natural product in Dictyopteris oils was determined as (+) - (3S,4S) with ca.100% enantiomeric exce